Polymerization catalysts, and in particular polymerization catalysts of the Ziegler-Natta type, currently comprise typically an inert support on which the actual active catalyst component, or a mixture or complex made up of catalytic compounds, is deposited. The chemical composition of such a heterogenous catalyst system, its surface structure, morphology, particle size, and particle size distribution are very important for the activity of the catalyst and for the properties of the polymer obtained through the use of the catalyst. By using a very active catalyst it is possible to produce a polymer from which, owing to its purity, it is not necessary to remove catalyst residues.
Heterogenous catalyst systems of the type referred to above are currently often made up of a magnesium-based support which has been treated with a transition metal compound of the titanium halide type and often also with an electron donor compound. It is also known that the support may be given an advantageous chemical composition, surface structure, morphology, particle size, and particle size distribution by allowing it to crystallize as a complex of some of its crystal solvents.
In the process according to EP publication 65700 and U.S. publication 4,421,674, a titanium halide is reacted with a magnesium chloride catalyst in the form of microspheres, whereafter the reaction product particles are recovered by physical means and are mixed together with an organometallic cocatalyst compound. FI patent application 862459 discloses a process for the preparation of a support wherein the support complex made up of a support and a crystal solvent is melted to form a clear liquid. When the liquid is directed through a nozzle and an atomization chamber into a crystallization chamber cooled with a cold nitrogen gas, the support complex will crystallize as small spherical particles. When the support pre-treated in this manner is contacted with a titanium halide, a large amount of catalytically active complexes between MgCl.sub.2 and the titanium halide are formed on the surface of the support as the crystal solvent is eliminated.